366 BALANIDiE. 



little apparent ; sometimes there is more than a single row of pores. 

 The points of the septa on the basal edge of the shell are small. The 

 internal surface of the shell is smooth. The sheath is closelv attached 



■r 



to the walls, and descends nearly to the basis ; on each side its lines 

 of growth are slightly upturned. The basis is deeply cup-formed or 

 cylindrical, and in section oval like the shell ; it penetrates the coral to 

 a very remarkable depth, — in one instance to three inches. The shelly 

 layer forming it, is thin, finely furrowed, and not permeated by pores. 

 This is the largest species in the genus ; one specimen was three quarters 

 of an inch in its longer diameter, and above three inches in length. 



The Scuta and Terga are calcified together, without any trace of a 

 suture; the line of junction can be inferred only from the analogy of 

 P. conjugatum, in which species the valves have a more normal 

 character, and are separated by a slight furrow. It may be seen in the 

 figure (PL 13, fig. 1 d) of the right and left hand opercular valves, 

 viewed from vertically above in their proper relative positions, how ab- 

 normal their appearance is, which is partly caused by the spinose 

 occludent ledges, presently to be described, but chiefly from the carinal 

 margins of the two terga not being straight and parallel, as in all other 

 cirripedes, and therefore not meeting each other, as is usual. In other 

 genera, only the upper part of the carinal margin of the two terga can be 

 opened for the exsertion of the cirri, the lower portion being united by 

 membrane ; but here, I have little doubt, from the position of attach- 

 ment of the adductor muscle (fig. 1 c), so close to and almost on the 

 terga, that the whole length of the carinal margin of the two terga 

 is free or disunited for the protrusion of the cirri. This opening be- 

 tween the two terga evidently cannot be closed, but is probably filled up, 

 and the animal thus protected, by the dorsal surfaces of the curled-up 

 cirri ; such, I believe, being likewise the case with some pedunculated 

 cirripedes, as with Conchoderma. The scutum has a large adductor plate, 

 which extends some little way (namely, about one quarter of the height 

 of the valve), below the ordinary basal margin. This latter margin is 

 slightly sinuous, and a little hollowed out towards the tergal corner of 

 the valve. I believe that the ridge, which runs down to the basi-scutal 

 corner of the tergum, though appearing to be part of the scutum, really 

 belongs to the tergum. The adductor scutorum plate is not, as in the 

 last two species, produced into a point at the rostral angle : at the tergal 

 end it blends into the under surface of the tergum. The occludent 

 margin is coarsely toothed. Rather on the under side of this margin 

 and in the upper part, there is a narrow occludent ledge, which extends 

 up beyond the apex of the valve, and thence runs a little way along the 

 carinal margin of the tergum, This ledge is thickly clothed with 

 strong, yellowish-brown spines, and hence appears like a brush. It is 

 remarkable that the cavity for the adductor scutorum muscle is situated 

 almost on the tergum. 



The tergum is of large size, and nearly square ; it is, in appearance, 

 separated from the scutum by a ridge running up to the apex. The 

 basal margin forms a right angle with the carinal margin, along which 

 latter margin the lines of growth are upturned, and blend into the 

 occludent ledge, which is common to the two valves. There cannot be 



